Thredded, the best Rails forums engine, has just released v0.5.0. This is a major release that adds topic subscriptions and a basic moderation system. Check out the live demo at thredded.org.

Some of the features currently in Thredded:

• Markdown post formatting with some BBCode support (by default).
• (Un)read posts tracking.
• Email notifications, topic subscriptions, @-mentions, per-messageboard notification settings.
• Private group messaging.
• Full-text search using the database.
• Pinned and locked topics.
• List of currently online users, for all forums and per-messageboard.
• Flexible permissions system.
• Basic moderation.
• Lightweight default theme configurable via Sass.